G recommendations A
series of standards defined by the ITU-TS covering transmission
facilities. They are: G.703 2.048Mbit/s - transmission facilities
running at 2.048Mbit/s that use the ITU-TS recommended physical
and electrical interface specified in G.703; G.703 641K - likewise
for transmission facilities running at 64Kbits/s; G.703 - the
ITU-TS standard 1984 current version for the physical and logical
traits of transmissions over digital circuits. G.703 now includes
specifications for the US 1.544Mbit/s as well as the European
2.048Mbit/s, and circuits with larger bandwidths on both continents.
G.703 is still generally used to refer to the standard for 2.048Mbit/s;
G.821 - ITU-TS Recommendation that specifies performance criteria
for digital circuits for ISDN.
Gateway Network interconnection
device and software that operate at OSI Layer Seven. A gateway
supports a full stack of the relevant protocol, such as SNA, DecNet,
ISO, TCP/IP, and can covert to a non-seven layer protocol, such
as async or BSC. It is typically used to provide access to wide
area networks over asynchronous or X.25 links from a LAN environment.
Examples include pads and protocol converters.
GFI (Group Format Identifier) (X.25
reference) the first four bits in a packet header, GFl contains
the obit, Dbit and modulus value.
GGP (Gateway-to-Gateway Protocol) The
protocol that core gateways use to exchange routing information,
GGP implements a distributed shortest path routing computation.
Gosip (Government Open Systems Interconnect
Profile) Country specific ISO OSI functional
profiles that have been defined as part of national procurement
policies. The US has US Gosip which is defined as a Federal Information
Processing Standard. The UK has the UK Gosip which is defined
by the Central Computer and Telecommunications Agency. The UK
Government will not buy equipment unless it supports OSI as specified
in Gosip. Unfortunately, the various Gosips as published by the
UK, US and Japanese governments are all slightly different.
GSM (Global System for Mobile communications)
A two-way, pan-European digital cellular
system. Its specification is in line with ISDN and ITU-TS System
7 signaling and approved by almost all European countries. GSM
operates at 900MHz and is a forerunner to the mass-market Personal
Communications Networks, based on the same set of standards. GSM
services include current digital subscriber services and the unique
Short Message Service - a superior form of paging offering up
to 160 alphanumeric characters with guaranteed delivery.
GUI (Graphical User Interface) Often
pronounced "goo-ee", it describes the screen display
that first greets a user and with which the user interacts during
the computer session. A GUI makes use of Windows, Icons, Menus
and Pointers - so-called WIMP systems - such as Microsoft Windows,
GEM and X-Windows. Apple's GUI is particularly notable and be-spoke
GUIs are becoming popular.
Group In the context
of network security, a group is a set of users who share common
permissions for one or more resources. Individually assigned user
permissions take precedence over those assigned through groups.
Guard band The unused
bandwidth separating channels to prevent crosstalk.
Guard tone A tone
generated by a high speed modem dial-up modem to ensure that there
is sufficient bandwidth available on the PSTN circuit for transmission.
